The invention relates to a manual device for the detection of photometric data which includes a measuring head, a source of light, optical illumination means to illuminate a measuring surface to be examined by the manual device, optical measuring means to capture the measuring light reflected by the measuring surface, and an optoelectronic layout exposed to the measuring light for the conversion of optical signals into data that may be displayed by a display unit.
A reflecting manual densitometer for the graphical industry is known from U.S. Pat. No. 4,645,350 and makes it possible to illuminate by means of a projecting measuring head a measuring surface and to determine the intensity of the light reflected by the measuring surface after its passage through a selectable measuring filter, in order to determine the reflectivity or density of a printing ink. The replaceable measuring filters are located in a filter wheel, which may be rotated with the aid of a motor so that all four measuring filters present may be introduced into the path of the measuring beam. In this manner the densitometer may be used for four different spectral ranges.
From German Patent Publication No. 3,313,668 a color measuring device is known, in which the measuring head and an evaluating unit are combined in a single structural unit, with a rechargeable energy source as the power supply. By the combination of these two components in a single structural unit without a connecting cable between the measuring head and the evaluating unit a certain miniaturization and easier handling are obtained.
However, the known color measuring device is relatively voluminous and greatly restricted in its applications. To recharge the source of power, it is set onto a charger, which together with the unit formed by the measuring head and the evaluating unit constitutes a single separable unit.
European Patent Publication No. 0,242,725 describes a spectral photometer, which may be located at a large distance from the measuring surface and which includes a source of light with its associated illumination optics as a first structural unit, and which evaluates the reflected light by means of a second structural unit. Although both units are located in a single housing adjacent to each other, in view of the large distance to the measuring surface desired, a particularly compact configuration of the second unit is not important; said second unit containing a polychromator with a diffraction grating. Because the diffraction grating is in the form of a planar diffraction grating, optical collimator means are required between the grating and a row of photodiodes. In place of the row of photodiodes a single photodiode may also be provided, if the dispersive element is variable. The dispersive element, which is in the form of a diffraction grating or a prism, is provided on the side of light incidence with collimator optics, so that the known polychromator is relatively large in view of the collimator optics and is not suitable for a manual device.
Holographically produced concave reflection gratings are known from "Proceedings of the Society of Photo-Optical Instrumentation Engineers", Vol. 24U, Periodic Structures, Gratings, Moire Patterns and Diffraction Phenomena, Jul. 29-Aug. 1, 1980, San Diego, S.P.I.E., 1980, (Bellingham, Washington, U.S.), J. M. Lerner, "Diffraction Gratings, Ruled and Holographic--a Review", pages 82-88. How such gratings may be used in the miniaturization of a manual device for the determination of optical reflection properties, is not described or discussed in the review article.
U.S. Pat. No. 4,093,991 discloses a spectral photometer with a monochromator, the outlet light of which supplies an optical sensor connected with a microcomputer comprising a keyboard. As an integration sphere is associated with the source of light and the monochromator, the configuration of the optical components is rather voluminous. The monochromator is connected with a coding device which makes it possible for the microcomputer to carry out a digital wavelength selection. The monochromator has a disk shaped interference wedge filter, the rotating position of which is correlated with the wavelength chosen. Together with the lens layout preceding and following it, a voluminous unit is obtained, which is suitable for laboratory use, but not for a miniaturized manual device.
In the article by M. Nordmeyer: "A simple measuring layout for the photoelectric spectrometry of the smallest possible concentrations", published in Spectrochimica Acta, Vol. 27B, No. 8, August 1972, Pergamon Press (Northern Ireland), an electronic circuit and an alternating method are described, whereby signal intensities at the location of a spectral line and of a representative underground location are measured photoelectrically and alternatingly. The electric circuit to carry out the alternating method contains two integrators.
In Elektrotechnik, Vol. 69, No. 3, Feb. 27, 1987 (Wurzburg), H. Hencke: "Distinction of very small differences", pages 28-38, a specially developed color sensor is described, which is capable of working very accurately and rapidly on a conveyor. The color sensor comprises an optical system which emits a white light to a measuring object and a red-green-blue photodiode receiving the light reflected by the measuring surface of the object, in order to produce an electrical analog signal. A control device is correlated with the color sensor; it contains a serial communication interface whereby for example the degree of browning of ceramic disks may be controlled by the color sensor.
A photoelectric color measuring device to determine color and density values is known from Patent Abstracts of Japan, Vol. 11, No. 370 (P-642) (2817), Dec. 3, 1987 and Japanese Patent Publication No. 62-142,240 (MINOLTA CAMERA CO.,LTD), Jun. 25, 1987. The photoelectric color measuring device contains a layout including a computer to process the data detected by the sensor unit. Different memories are provided for programs, color conversions and the storage of color and density information.
From Nouvelles Graphiques, Vol. 37, No. 2, January 1987 (Deurne, Antwerpen, BE) , "La nature connait ses imperfections (Nature knows its imperfections), Macbeth y pallie", p. 2, a portable and automatic manual densitometer is known, which comprises a computer, the programs of which make it possible to identify the color measured, the type of measuring surface and the paper used.
With this known manual device only densitometric evaluations are possible, but no determination of colorimetric values are possible.